(1) Field of the Invention
The present invention relates to an adhesive for polyester fibrous material, and more particularly relates to a novel adhesive capable of bonding strongly polyester fibrous material with rubber and having high resistance against deterioration during the use at high temperature.
(2) Description of the Prior Art
Polyester materials, such as polyethylene terephthalate and the like, which are linear polymers having ester linkages in the main chain, are superior to nylon material and the like in the retention of stable dynamic properties, for example, low stress relaxation, low creep property and good recovery after stretching. Therefore, polyester material is very advantageously used as a reinforcing material for rubber articles, such as tire, belt, air cushion, rubber hose and the like, in the form of a filament, yarn, cord, cable, cord fabric, canvas and the like.
However, polyester has a dense hyper-structure and a small number of functional groups, and therefore when it is intended to use polyester material as a reinforcing material for these rubber articles, polyester material cannot be satisfactorily bonded to rubber by means of RFL liquid comprising resorcin/formaldehyde initial condensate and rubber latex and being an adhesive capable of bonding strongly nylon material, rayon material and the like to rubber.
In order to obviate this drawback, there have hithereto been proposed a method, wherein polyester surface is treated with alkali or amine to increase the number of active groups, such as --OH, --COOH,--NR.sub.2 groups and the like, wherein R represents a hydrogen atom or an alkyl group, on the surface, and then the polyester is treated with RFL; and a method, wherein a functional group having a bonding ability with hydrogen or capable of forming primary bond is introduced into polyester surface by an isocyanate compound or epoxy compound, and then the polyester is treated with RFL; and various adhesive compositions used for these methods.
However, isocyanate compound and epoxy compound have a high reactivity and react with water and RF, which water is used as a solvent for RFL, and therefore it is difficult to use isocyanate compound or epoxy compound in a one-bath system adhesive liquid. In order to obviate this drawback, the treatment for polyester with the adhesive must be carried out in two stages. However, a more complicated installation and a larger amount of heat are required in the two stage treatment, and the two stage treatment is not preferable in view of the resource saving and energy saving. Moreover, epoxy compound and isocyanate compound fume in a large amount during the heat treatment, and are not preferable in view of environmental pollution and public nuisance. In addition, polyester fiber is hardened by a pretreatment with an epoxy compound or isocyanate compound, and it is difficult to treat the polyester fiber. As a result, rubber articles reinforced with polyester fibers treated with the adhesive containing an epoxy compound or isocyanate compound are short in the life, and when the rubber articles are used under high strain or at high temperature, the adhesive layer deteriorates rapidly.
As the adhesive to be used for treating polyester fibrous material in a two stage treatment, there has been proposed a combination system of RFL and a condensate obtained by reacting formaldehyde with a mixture of monohydric phenol and polyhydric phenol (Japanese Patent Laid-open Application No. 37,986/74). The inventors have made a follow-up test with respect to a m-cresol/resorcin/formaldehyde cocondensate and the like, which are typical cocondensates described in this Japanese patent laid-open application and found that adhesive using the cocondensate is still insufficient in the adhesive strength and is poor in the heat resistance.
While, as an adhesive for polyester fibrous materials, which can treat them in one stage in a one bath system, there has been proposed an adhesive, which uses a tricyclic cocondensate formed of a resorcin derivative and a phenol derivative in combination with RFL (Japanese Patent Application Publication No. 11,251/71). Cocondensates concretely disclosed in the Japanese Patent Application Publication No. 11,251/71 are cocondensates of resorcin or a resorcin derivative, such as alkylresorcin, o- or p-substituted alkyl- or halogeno-phenol and formaldehyde. These cocondensates are produced through a methylol compound formed by the reaction of a bifunctional o- or p-substituted alkyl- or halogeno-phenol with formaldehyde. Accordingly, the phenol ring of the resulting cocondensate has no longer electrophilically reactive site, and the cocondensate is poor in the reactivity with RF and RFL and is low in the adhesive strength.